Thermoplastics are often thermoformed by employing injection molding and blow molding techniques. Within these thermoforming operations, efficacy is often measured by cycle time, which may generally be referred to as the time required to manufacture a given part. A decreased cycle time is often advantageous inasmuch as a greater number of parts can be manufactured per unit time.
A factor often limiting cycle time is the characteristics of the thermoplastic material that is being thermoformed. In particular, the amount of time required for the thermoplastic material to cool from its melting temperature (Tm) to its crystallization temperature (Tc) is often the limiting step in the manufacturing process.
Attempts have been made to improve the rate of crystallization of thermoplastic resins used in thermoforming processes. For example, constituents that can act as a crystallization agent are often added to the thermoplastic resin. For example, U.S. Pat. No. 6,780,936 teaches diene-olefin copolymer nucleating agents that are advantageous in increasing the crystallization temperature of certain polyolefins. These copolymers derive from the copolymerization of α,ω-dienes and olefins by employing supported single-site catalyst systems.
The use of crystallization agents or nucleating agents can, however, have a deleterious impact on other features or properties of the thermoplastic resin.
Thermoplastic vulcanizates can advantageously be thermoformed. Because thermoplastic vulcanizates have many technologically useful features, they are often thermoformed into parts or articles where superior engineering properties are required. Therefore, any deleterious impact that may be imparted by a crystallization agent can often not be tolerated. Nonetheless, efficiencies in the thermoforming processes of thermoplastic vulcanizates are continually sought.
Copolymers of olefin and α,ω-dienes have been added to thermoplastic vulcanizates as disclosed in U.S. Pat. No. 6,433,090. These copolymers of olefins and α,ω-dienes, which are characterized by long-chain branches, are added in an amount from about 5 to about 75% by weight of the thermoplastic component of the thermoplastic vulcanizate in order to provide compositions that can be foamed into cellular materials that exhibit improved properties such as compression set and compression load deflection.
There is therefore a continued desire to improve the rate of crystallization of thermoplastic vulcanizates in order to enhance the thermoforming operations thereof without deleteriously impacting the other properties of the thermoplastic vulcanizate or thermoformed parts or articles thereof.